Process of desensitizing silver-bromide emulsions and plates or films covered with such emulsions



Patented May 27, 193% uurreo ,srArEsvParser orrica IBENNO EoMoLKA, DECEASED, LATE OF ERANKEoRr-oN-rHE-MAIN, GERMANY; BY

RUDOLF ROSENTHAL, EXECUTOR, 0F ERANK oREoN-rRE-MAIN, GERMANY, As- SIGNOR .ro '1. o. EARRENINnUs'rRI AKTIENeEs LLscHAEr, 0F ERANxEoR'r-oN- THE-MAIN, GERMANY, A CORPORATION OF GERMANY PROCESS OF DESENSITIZING SILVER-BROMIDE EMULSIONS AE'D PLATES OR FILMS COVERED WITH SUCH EMULSIONS No Drawing. Application filed December 20, 1927,

NH 3 i 6 M 5 in which Ac means the residue of an acid, that is to say 3-6-diamino-phenyhphcnazonium salts, forinstance the pheno-safranine and tolu-safranine, have the property of desensitizing photographic silver-bromide emulsions in such a degree that they can be developed in yellow light. The said dyestuffs have, however, the disadvantage that they stain the gelatin layer of the plates and films, the vessels and also the fingers and clothes of the operators, intensely red. Though in the case of photographic plates this color can be removed from their gelatin layer, this cannot be done with films, because the latter, when treated with safranine dyestuffs, are stained so much that they are entirely spoiled thereby and rendered unfit for use. For this reason the process of desensitizing by means of safranines cannot be applied in developing films.

The inventor has now found that the isomerides of the said safranine dyestufi's in which at least two amino groups are situated in one and the same carbon nucleus belonging to the azine complex, have a very strong desensitizing action upon photographic silver bromide emulsions. These compounds offer the advantage over the normal safranine dyestuffs that, in spite of their pronounced dyestuff character, they do not stain at all,

Serial No. 241,447, and in Germany. June 15, 1927.

or only very slightly, the gelatin layers, the fingers of the operator etc., so that the fihns or other materials are not spoiled, and the slight coloring imparted to them can be easily washed out by means of water. =For instance the following compounds of the said kind are suitable for producing this efl'ect:

in which Ac represents the residue of an acid (see Berichte der Deutschen Chem. Ges. Vol. 33 page 3074) the 2-3-diamino-phenyl-phenaz'onium salts of the formula:

in which Ac represents the residue of an acid (see'Helveti'ca Chimica Acta VIII page 27 9) and also the homologues and substitution products thereof, for instance the alkyl-, halogen-, amino-oxyalkyl derivatives or the like. v The photographic layers may be desensitized either by immersing the plates or films, before they are developed, for l-2 minutes into the solution of the iso-diamino-phenylphenazonium salt or by adding a small quantity of this compound to the developer.

The following examples serve to illustrate 1. The plate immersed into 1:5000) the invention but they are not intended to limit it thereto.

or film to be developed is an aqueous solution (about of 1-3-diamino-phenyl-phenazonium-chloride for about 1-2 minutes and the development can then be eflected in yellow 2. About 100 light or in candle light.

ccm. of the'developer are mixed with 2 com. of a solution (1:500) of 1 3 -diamino-phenyl-phenazonium-chloride.

After the plate in the developer development can or candle light.

3. In the processes set of the film has remained for about one minute, the be finished in yellow light forth in (Example 1) and (Example 2) there may be used 1n stead of the above named compound, for instance the following compounds: 1-3-diamino-7-aminophenyl phenazonium chloride; 2-3-diamino-phenyl-phenazonium-nitrate; 1-

3-diamino-6- (or 7 )-chlorphenyl-phenazomum-chloride; 1-3-diamino-ortho- (or para) tolyl-phenazonium-chloride of the following formula CH; (ortho) 1-3-diamino-ortho- (or p a r a) -o x y a l k y lphenyl-phenazonium-chloride; 1-3-diamino- 6-oxyalky-phenyl-phenazonium-chloride of the formula:

What is claimed is:

1. The process of desensitizing photographic silver-bromide layers, which consists in treating the phenylphenazonium two amino groups layer with an amine of a salt in which at least are situated in one and the same carbon ring belonging to the azine complex. 7

2. The process of desensitizing photographic silver-b romide layers, which consists in treating the layer with a salt of a phenylphenazonium of the following composition:

In testimony whereof, I aflix my si nature.

RUDOLF ROSENTIIAL, Executor of the Estate of Ben/no H omollaw,

Deceased. 

